A fiber reinforced composite material (e.g. carbon fiber reinforced plastic: CFRP) composed of a fiber component and a resin component is sometimes used for a skin of a main wing member of an aircraft and so on. A stringer (a longitudinal material) is sometimes attached to the skin to improve strength of the skin. The skin to which the stringer is attached is hereinafter referred to as a reinforcing structure. The fiber reinforced composite material is sometimes used for the stringer, like the skin.
Upon manufacturing the reinforcing structure, a cured stringer is arranged on an uncured skin through adhesive. Next, the skin is cured by use of heat and pressure and the stringer is bonded with the skin as a unitary body.
The cured stringer is sometimes processed to adjust its size before being bonded with the skin. When the processing is carried out, the fiber component is exposed in a processed surface. That is, a fiber exposure surface is formed in a part of the stringer.
A current or voltage is sometimes applied to the reinforcing structure in the operation. For example, when the reinforcing structure is used for the main wing member of the aircraft, a lighting current or a high voltage is sometimes applied to the reinforcing structure due to a thunder. When the fiber exposure surface exists, an edge glow discharge sometimes occurs with the applied current or voltage.
A technique of preventing the edge glow discharge is disclosed in Patent Literature 1 (US 2008/0128430A1). In Patent Literature 1, to seal up the fiber exposure surface with a thermosetting resin layer and to cure the sealed resin layer are disclosed.